Bug Computercraft: bios:339: [string "filemanager"]:13: 'then' expected

[exos9]

So I typed a quick program to test some functions in my OS and when creating an "Exit" button I came across something weird... I'm still learning but I find this weird:

term.setBackgroundColor(2048)
term.setTextColor(1)
term.clear()
term.setCursorPos(12,1)
print("Welcome to the file manager")
term.setCursorPos(5,2)
print("Here are the commands you can enter:")
shell.run("help")
term.setCursorPos(20,13)
shell.run("ls")
term.setCursorPos(23,19)
print("Exit")
if X>=23 and X<=28 and Y=18 and button == 1 then
shell.run("gui")
end

When I try to run it I get the error : bios:339: [string "filemanager"]:13: 'then' expected
I'm stumped.. Could anyone help me? Bear in mind I'm not that good at coding yet